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United States Department of Agriculture

Agricultural Research Service

Research Project: INTEGRATION OF CLIMATE VARIABILITY AND FORECASTS INTO RISK-BASED MANAGEMENT TOOLS FOR AGRICULTURE PRODUCTION AND RESOURCE CONSERVATION

Location: Great Plains Agroclimate and Natural Resources Research Unit

Title: Sediment transport and soil detachment on steep slopes: II. Sediment feedback relationship

Authors
item Zhang, Guang-Hui - BEIJING UNIV, CHINA
item Liu, Yu-Mei - BEIJING UNIV, CHINA
item Han, Yan-Feng - BEIJING UNIV, CHINA
item Liu, Bao-Yuan - BEIJING UNIV, CHINA
item ZHANG, XUNCHANG

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 2008
Publication Date: July 1, 2009
Citation: Zhang, G., Liu, Y., Han, Y., Liu, B., Zhang, X.J. 2009. Sediment transport and soil detachment on steep slopes: II. Sediment feedback relationship. Soil Science Society of America Journal. 73(4):1298-1304.

Interpretive Summary: Understanding the effect of sediment concentration or load on soil detachment rate is important for understanding soil erosion processes and for developing process-based soil erosion models. Many studies conducted in recent years attempted to quantify the feedback relationship between sediment concentration and detachment rate. However, to date the effects of sediment load on detachment rate are still unclear. The goals of this study were to examine the effects of sediment concentration on soil detachment rates by flowing water and to further quantify their relationships under controlled flume conditions. Experiments were carried out in a hydraulic flume, with slope gradients ranging from 8.8% to 46.6% and flow rate per unit width from 0.0013 to 0.005 square meters per second. Soil detachment rates were measured under different sediment concentrations, which were 0% (clear water), 25%, 50%, 75%, and 100% of the maximum sediment concentration that a flow can carry. Results showed that detachment rates decreased as sediment concentration increased, and the relationship could be adequately described with a linear equation for most cases. Overall results indicated that the linear equation proposed by Forster and Meyer (1972) was adequate to describe the effect of sediment concentration on soil detachment. The results are useful to erosion modelers for developing and fine-tuning process-based soil erosion prediction tools, which can be used by soil conservationists to conserve soil and water resources.

Technical Abstract: Quantifying the effect of sediment load on detachment rate is crucial to understand soil erosion processes and to develop physically-based soil erosion models. Many studies conducted in recent years attempted to quantify the feedback relationship between sediment concentration and detachment rate. However, to date the effects of sediment load on detachment rate are still unclear. The objectives of this study were to examine the effects of sediment load on detachment rates and to verify the quantitative relationship between sediment load and detachment rate in rills under controlled conditions. Experiments were carried out in a hydraulic flume with constant roughness. Slope gradient (S) varied from 8.8% to 46.6% and unit flow rate (q) from 0.00125 to 0.005 square meters per second. Detachment rates were measured under different sediment loads, which were 0% (clear water), 25%, 50%, 75%, and 100% of sediment transport capacity (Tc) for 20 combinations of q and S. Tc was measured in the same flume with two sediment sources to ensure that transport capacity was reached for each combination of q and S. Results showed that detachment rates decreased as sediment load increased. Discrepancies in declining patterns of detachment rates were observed. Regression results indicated that 16 combinations of q and S were well simulated by linear feedback relationships, while four combinations were best fitted to exponential functions. Both predicted detachment capacity (Dc) and Tc by linear relationships agreed well with the corresponding measured values (model efficiency is 0.97 for Dc and 0.98 for Tc). The predicted detachment rate by first-order coupling equation proposed by Forster and Meyer (1972) agreed with measured data well (model efficiency=0.92). This result indicated that the feedback relationship between sediment load and detachment rate in this flume study could be satisfactorily described by the first-order coupling equation.

Last Modified: 9/10/2014
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